Sildenafil, of structural chemical formula: ##STR1##
is known, from e.g. European Patents EP-A-0463756 and EP-A-0812845. It has pharmaceutical utility in the treatment of male sexual dysfunction.
As a relatively complicated synthetic organic chemical molecule, sildenafil requires a multi-step chemical synthesis.
Any organic synthesis step, which is part of a complex multi-step synthesis, results in contamination of the intermediate with solvents, catalysts, starting materials and by-products and so introduces the requirement for purification. If a pharmaceutical grade of final product is to result, this cleaning must be done either as the contamination is caused, that is in the work-up of the particular step, or at some subsequent point in the process. A rugged process is desirable which is not demanding with regard to the purity of the intermediates and which allows for a very efficient cleaning during the isolation of the final drug product.
It is an object of the present invention to provide novel processes for preparing sildenafil which simplify the purification procedures and which produce sildenafil in substantially pure form without involving complex purification procedures.
It is a further object of the present invention to provide intermediates useful for the preparation of sildenafil by such novel processes.